Electrochemical characterization and immersion corrosion of a consolidated silver dental biomaterial Mueller, H. J. and R. W. Hirthe (2001), Biomaterials 22(19): 2635-46.Abstract: A consolidated silver (CS) material, an alternative to dental amalgam, was studied for corrosion. Chemically precipitated silver particles were acid activated and pressure consolidated to a volume porosity of 25%. In selected tests comparisons were made between CS and melted and cast silver particles (MS), silver with a known mass fraction purity of 99.998% (FS), a silver-palladium alloy (SP). and a dispersed-phase amalgam (DA). Fusayama artificial saliva was used with controlled variations in pH, sulfide content, mucin content, and absorbed oxygen content. Electrochemical polarization, electrochemical impedance spectroscopy, and immersion methods were used. Results revealed differences in the zero current potentials E(I = 0) from forward polarization between CS and MS (or FS) in deaerated solution. By superposition of the cathodic polarization curves, the area for CS was increased by 7.3 times and was enclosed within an outer shell of material 5.5 microm thick. Polarization resistance was significantly the highest for SP, followed in order by MS (or FS) and CS or DA. With scanning electron microscopy, CS was shown to be significantly more susceptible than MS to long-term immersion corrosion. The modeled equivalent electrical circuits for CS and DA involved a double layer capacitance, a charge transfer resistance, and an element attributed to adsorption. The active pore depth for CS from the transmission line model for porous solids revealed satisfactory agreement with polarization results. It is concluded that the corrosion susceptibility of CS in Fusayama solution, while similar to that for DA, is greater than it is for MS.

Electrochemical corrosion and metal ion release from Co-Cr-Mo prosthesis with titanium plasma spray coating Reclaru, L., P. Y. Eschler, et al. (2005), Biomaterials 26(23): 4747-56.Abstract: The corrosion behavior of CoCrMo implants with rough titanium coatings, applied by different suppliers by either sintering or vacuum plasma spraying, has been evaluated and compared with uncoated material. The open-circuit potential, corrosion current and polarization resistance were determined by electrochemical techniques. The Co, Cr and Ti ions released from the samples into the electrolyte during a potentiostatic extraction technique were analyzed using ICP-MS. The Ti coatings from the different suppliers showed a different porous morphology, and the implants exhibited a distinct corrosion activity, underlining the importance of the coating process parameters. Among the titanium coated samples, the one with the sintered overcoat turned out to be the most resistant. Yet, on an absolute scale, they all showed a corrosion resistance inferior to that of uncoated CoCrMo or wrought titanium.

Electrochemical corrosion of metallic biomaterials Pourbaix, M. (1984), Biomaterials 5(3): 122-34.Abstract: Methods of electrochemical thermodynamics (electrode potential-pH equilibrium diagrams) and electrochemical kinetics (polarization curves) may help to understand and predict the corrosion behaviour of metals and alloys in the presence of body fluids. A short review of the literature is given concerning some applications of such methods, both in vitro and in vivo, relating to surgical implants (stainless steels, chromium-cobalt-molybdenum alloys, titanium and titanium alloys) and to dental alloys (silver-tin-copper amalgams, silver-base and gold-base casting alloys, nickel-base casting alloys). Attention is drawn to the necessity of more basic research on crevice- and fretting-corrosion of surgical implant materials and dental alloys, and to the toxicity of corrosion products. A perfect understanding of the exact significance of electrode-potentials is essential for the success of such a task.

Electrochemical impedance spectroscopy study of Ti-6Al-4V alloy in artificial saliva with fluoride and/or bovine albumin Huang, H. H. and T. H. Lee (2005), Dent Mater 21(8): 749-55.Abstract: OBJECTIVES: To investigate the electrochemical mechanism of Ti-6Al-4V alloy in acidic artificial saliva with NaF and/or bovine albumin (BA). METHODS: The electrochemical behavior of Ti-6Al-4V alloy was investigated using electrochemical impedance spectroscopy (EIS) measurements at the open circuit potentials. The electrolytes used included artificial saliva with 0-0.5% NaF, with 0.1% NaF+0.01-0.5% BA, and with 0.01-0.5% BA at pH 5 and 37 degrees C. One-way ANOVA was used to analyze the influence of NaF and BA concentration on the polarization resistance (Rp) obtained from the EIS data. Surface chemical analyses were performed with X-ray photoelectron spectroscopy. RESULTS: The impedance was mainly characterized by the resistance and capacitance of a protective TiO2-based passive film on Ti-6Al-4V alloy when NaF concentration was low (< or = 0.01%). When NaF concentration was higher than 0.1%, the impedance was characterized by two capacitive and one inductive effects, which were related to the metal's charge transfer reaction and the decayed TiO2-based oxide film (capacitive effects), and the relaxation of the adsorbed Ti-F complex compound (inductive effect). The addition of 0.01-0.5% BA in 0.1% NaF-containing artificial saliva significantly increased the impedance of Ti-6Al-4V alloy compared to that without BA addition (p < 0.001). The presence of BA in fluoride-free artificial saliva had no influence on the electrochemical impedance of Ti-6Al-4V alloy (p > 0.05). SIGNIFICANCE: The EIS measurement technique is suitable for the study of the electrochemical behavior of dental alloy. The electrochemical mechanism of Ti-6Al-4V alloy in artificial saliva is related to the fluoride and bovine albumin concentration.

Electrochemical studies on zirconium and its biocompatible alloys Ti-50Zr at.% and Zr-2.5Nb wt.% in simulated physiologic media Oliveira, N. T., S. R. Biaggio, et al. (2005), J Biomed Mater Res A 74(3): 397-407.Abstract: Different electrochemical studies were carried out for Zr and its biocompatible alloys Ti-50Zr at.% and Zr-2.5Nb wt.% in solutions simulating physiologic media, Ringer and PBS (phosphate buffered saline) solutions. The results from rest-potential measurements showed that the three materials are spontaneously passivated in both solutions and that the Ti-50Zr alloy has the greatest tendency for spontaneous oxide formation. Some corrosion parameters (such as the pitting and repassivation potentials) were obtained via cyclic voltammetry in both solutions, revealing that the Ti-50Zr has the best corrosion protection while Zr has the worst. On the other hand, the pre-anodization (up to 8 V vs. SCE) of the alloys in a 0.15 mol/L Na2SO4 solution led to a significant improvement in their protection against pitting corrosion when exposed to the Ringer solution. Elemental analyses by EDX showed that during pitting corrosion, there is no preferential corrosion of any of the alloying elements (Zr, Ti, Nb).

Electrochemistry of galvanic couples between carbon and common metallic biomaterials in the presence of crevices Silva, R. A., M. A. Barbosa, et al. (1990), Biomaterials 11(5): 336-40.Abstract: In vitro experiments were conducted upon some common metallic biomaterials and carbons, both isolated or forming galvanic couples, in a cell specially designed for crevice corrosion studies. The alloys examined were AISI 316L stainless steel, Ti6AI4V and Co-Cr-Mo. The types of carbon were glassy carbon and carbon fibre-reinforced carbon. The surface modifications were evaluated by SEM, AES and ESCA-XPS analyses. AISI 316L stainless steel suffered localized corrosion in open-circuit experiments whilst the other materials remained unattacked. Galvanic currents between metal-carbon couples were measured by zero resistance ammetry. The carbon-metal area ratio was 1:1. The results showed that 316L stainless steel and the Co-Cr-Mo alloy were prone to accelerated corrosion, whilst the Ti6AI4V alloy remained unattacked. The galvanic corrosion currents were also predicted using mixed potential theory from polarization curves obtained for each material. The experimental and theoretical values showed good agreement for the stainless steel and Co-Cr-Mo alloy. Long-term immersion tests with the same couples showed that the only metal not to suffer degradation was the Ti6AI4V alloy.

Electron beam irradiation as protection against the environmental release of recombinant molecules for biomaterials applications Gold, R. S., J. Maxim, et al. (2005), J Biomater Sci Polym Ed 16(1): 79-89.Abstract: In biomaterials applications there exists a need to protect against the environmental release of recombinant microorganisms and transmissible genetic material and to prevent the recovery of proprietary genetic information. Irradiation technologies have long been used to eliminate microorganisms associated with spoilage and contamination and recent studies have demonstrated that moderate doses of irradiation may be used to sterilize medically important proteins without causing adverse effects in their desirable biological properties. Recombinant Escherichia coli cells expressing organophosphate hydrolase (OPH, E.C. 3.1.8.1), an important enzyme for the detection and decontamination of neurotoxic pesticides and chemical warfare agents, were subjected to electron beam irradiation to gauge its effect on enzymatic activity, cell viability and DNA recoverability. Bacterial samples were irradiated at 2, 20 and 200 kGy using a 10 MeV electron source. Irradiation levels of 2 to 20 kGy were sufficient to eliminate viable cells without affecting OPH enzymatic activity. Biologically active DNA was recovered via PCR from all samples through the 20 kGy irradiation level. While DNA was not recovered from samples at the 200 kGy exposure level, protein activity was reduced by 19 to 78%, depending on the method of cell preparation. These results demonstrate that irradiation can be effective in preventing the release of recombinant organisms intended for use in biomaterials applications without eliminating enzymatic activity and suggests that further research may indicate specific conditions whereby DNA recovery can be eliminated while retaining sufficient enzymatic activity for targeted biomaterials applications.

Electronic nose screening of ethanol release during sol-gel encapsulation A novel non-invasive method to test silica polymerisation Lovino, M., M. F. Cardinal, et al. (2005), Biosens Bioelectron 21(6): 857-862.Abstract: Porous silica matrices prepared by sol-gel process yield biocompatible materials adequate for encapsulation of biomolecules or drugs. The procedure is simple and fast, but when alkoxyde precursors like tetraethoxysilane (TEOS) are used the polymerisation reaction leads to the formation of alcohol as a by-product, which can produce undesirable effects on the activity of entrapped enzymes or modify a drug release kinetic. Therefore, it is critical to determine that no remnant ethanol is left prior using or storing the obtained biomaterial. In this regard, the technique used in the alcohol determination should be non-invasive and non-destructive to preserve the encapsulation device intact and ready to use. In this work we have successfully used a portable electronic nose (e-nose) for the screening of silica polymerisation process during theophylline encapsulation. TEOS reaction was "smelt" since precursor pre-hydrolysis until the end of ethanol release, sensed directly at the headspace of matrices slabs. Measurements showed that ethanol was negligible since 10th day in polymeric slabs of 10mm width and 2cm diameter. This first use of e-nose following a polymerisation reaction opens a wide number of putative applications in pharmaceutical and biochemical fields.

Electrophoretic and thermodynamic properties for biomaterial particles with Bovine Serum Albumin adsorption Sanchez-Munoz, O. L., E. G. Nordstrom, et al. (2003), Biomed Mater Eng 13(2): 147-58.Abstract: The main purpose of our investigation is to achieve better insight into the electrophoretic and thermodynamic properties of protein-coated biomaterial particles. Many academic studies have been performed to understand the complex phenomena of microscopic biomaterial particles as a function of ionic strength, pH and temperature. By electrophoretic measurements of biomaterial particles, the surface structures of it can be analysed with a suitable model. Therefore, the zeta potential measurements are useful to know the effects of adsorbed BSA concentration upon the electrophoretic properties of bioceramics and bioglasses. Unexpectedly, the zeta potential of the BSA-coated biomaterials exhibits a local minimum as the concentrations of adsorbed BSA increases. Apparently, the structures of the attached BSA layer on the biomaterial particles play a significant role. In an attempt to elaborate the phenomenon observed, a model for proteins, which composes two BSA sublayers with different structures and properties, is proposed. Also, the association or equilibrium constant were determined and represented the isotherm curves in function of the zeta potential measurements.

Electropolymerized films formed from the amphiphilic decyl esters of d- and l-tyrosine compared to l-tyrosine using the electrochemical quartz crystal microbalance Marx, K. A., T. Zhou, et al. (2005), Biomacromolecules 6(3): 1698-706.Abstract: Using the electrochemical quartz crystal microbalance (EQCM), we compared thin films formed on Pt by electropolymerization of l-tyrosine to that of the amphiphilic monomers, decyl esters of d- and l-tyrosine (DEDT and DELT). Mass build-up and film properties were determined as a function of monomer concentration via frequency, f, motional resistance, R, and charge passage, Q, measurements. Films were found to occur by a combination of monomer electropolymerization and adsorption for DEDT and DELT, but only by electropolymerization for l-tyrosine. This difference in film formation process for the monomers is reflected in the net mass build-up for each film, as represented by calculated df/dQ values. For the adsorbing monomers DEDT and DELT, films possessed concentration dependent df/dQ values, more than 100-fold greater than that for l-tyrosine film formation under equivalent electropolymerization conditions. During the entire film growth process, all three films exhibited no significant energy dissipation properties (DeltaR invariant). Concentration dependent adsorption of significant levels of unpolymerized but self-assembled DEDT and DELT monomers account for the subsequent time dependent mass loss observed from the films maintained in buffer in the absence of monomer. Contact angle measurements demonstrated a pH dependent increase in the surface hydrophilicity of films electropolymerized from the DEDT, DELT, and l-tyrosine monomers but not films formed from phenol and 3-nitrophenol monomers. This behavior is consistent with the monomers' known changes in titration/charge state properties with increasing pH. This study provided insight into the film formation, stability, and surface hydrophilicity resulting from electropolymerization of these related tyrosine based monomers. This information is critical to assessing the utility these films may have in the development of new biomaterials and as biological macromolecule or cell immobilization strategies in biosensors.

Electrospinning of chitosan dissolved in concentrated acetic acid solution Geng, X., O. H. Kwon, et al. (2005), Biomaterials 26(27): 5427-32.Abstract: Chitosan nanofibers were electrospun from aqueous chitosan solution using concentrated acetic acid solution as a solvent. A uniform nanofibrous mat of average fiber diameter of 130 nm was obtained from the following optimum condition: 7% chitosan solution in aqueous 90% acetic acid solution was successfully electrospun in the electric field of 4 kV/cm. The aqueous acetic acid concentration higher than 30% was prerequisite for chitosan nanofiber formation, because more concentrated acetic acid in water progressively decreased surface tension of the chitosan solution and concomitantly increased charge density of jet without significant effect on solution viscosity. However, acetic acid solution more than 90% did not dissolve enough chitosan to make spinnable viscous concentration. Only chitosan of a molecular weight of 106,000 g/mol produced bead-free chitosan nanofibers, while low- or high-molecular-weight chitosans of 30,000 and 398,000 g/mol did not. Average fiber diameters and size distribution decreased with increasing electric field and more bead defects appeared at 5 kV/cm or more.

Electrospun chitosan-based nanofibers and their cellular compatibility Bhattarai, N., D. Edmondson, et al. (2005), Biomaterials 26(31): 6176-84.Abstract: Chitosan-based nanofibers with an average fiber diameter controllable from a few microns down to approximately 40 nm and a narrow size distribution were fabricated by electrospinning solutions containing chitosan, polyethylene oxide (PEO), and Triton X-100. Rheological study showed a strong dependence of spinnability and fiber morphology on solution viscosity and thus on chitosan-to-PEO ratio. The nanofibers can be deposited either as a nonwoven mat or as a highly aligned bundle of controllable size. Potential use of this nanofibrous matrix for tissue engineering was studied by examining its integrity in water and cellular compatibility. It was found that the matrix with a chitosan/PEO ratio of 90/10 retained excellent integrity of the fibrous structure in water. Experimental results from cell stain assay and SEM imaging showed that the nanofibrous structure promoted the attachment of human osteoblasts and chondrocytes and maintained characteristic cell morphology and viability throughout the period of study. This nanofibrous matrix is of particular interest in tissue engineering for controlled drug release and tissue remodeling.

Electrospun fine-textured scaffolds for heart tissue constructs Zong, X., H. Bien, et al. (2005), Biomaterials 26(26): 5330-8.Abstract: The structural and functional effects of fine-textured matrices with sub-micron features on the growth of cardiac myocytes were examined. Electrospinning was used to fabricate biodegradable non-woven poly(lactide)- and poly(glycolide)-based (PLGA) scaffolds for cardiac tissue engineering applications. Post-processing was applied to achieve macro-scale fiber orientation (anisotropy). In vitro studies confirmed a dose-response effect of the poly(glycolide) concentration on the degradation rate and the pH value changes. Different formulations were examined to assess scaffold effects on cell attachment, structure and function. Primary cardiomyocytes (CMs) were cultured on the electrospun scaffolds to form tissue-like constructs. Scanning electron microscopy (SEM) revealed that the fine fiber architecture of the non-woven matrix allowed the cardiomyocytes to make extensive use of provided external cues for isotropic or anisotropic growth, and to some extent to crawl inside and pull on fibers. Structural analysis by confocal microscopy indicated that cardiomyocytes had a preference for relatively hydrophobic surfaces. CMs on electrospun poly(L-lactide) (PLLA) scaffolds developed mature contractile machinery (sarcomeres). Functionality (excitability) of the engineered constructs was confirmed by optical imaging of electrical activity using voltage-sensitive dyes. We conclude that engineered cardiac tissue structure and function can be modulated by the chemistry and geometry of the provided nano- and micro-textured surfaces. Electrospinning is a versatile manufacturing technique for design of biomaterials with potentially reorganizable architecture for cell and tissue growth.

Electrospun protein fibers as matrices for tissue engineering Li, M., M. J. Mondrinos, et al. (2005), Biomaterials 26(30): 5999-6008.Abstract: Electrospinning has recently emerged as a leading technique for generating biomimetic scaffolds made of synthetic and natural polymers for tissue engineering applications. In this study, we compared collagen, gelatin (denatured collagen), solubilized alpha-elastin, and, as a first, recombinant human tropoelastin as biopolymeric materials for fabricating tissue engineered scaffolds by electrospinning. In extending previous studies, we optimized the shape and size (diameter or width) of the ensuing electrospun fibers by varying important parameters of the electrospinning process, such as solute concentration and delivery rate of the polymers. Our results indicate that the average diameter of gelatin and collagen fibers could be scaled down to 200-500 nm without any beads, while the alpha-elastin and tropoelastin fibers were several microns in width. Importantly, and contrary to any hitherto reported structures of electrospun polymers, fibers composed of alpha-elastin, especially tropoelastin, exhibited "quasi-elastic" wave-like patterns at increased solution delivery rates. The periodicity of these wave-like tropoelastin fibers was partly affected by the delivery rate. Atomic force microscopy was utilized to profile the topography of individual electrospun fibers and microtensile testing was performed to measure their mechanical properties. Cell culture studies confirmed that the electrospun engineered protein scaffolds support attachment and growth of human embryonic palatal mesenchymal (HEPM) cells.

Electrostatic interactions as a predictor for osteoblast attachment to biomaterials Smith, I. O., M. J. Baumann, et al. (2004), J Biomed Mater Res A 70(3): 436-41.Abstract: The present study utilizes zeta (zeta)-potential analysis as an indicator of bonding of osteoblasts and whole bone to various biomaterials. Common metal alloys (316L stainless steel, CoCrMo, and Ti6Al4V) and bioceramics (hydroxyapatite and beta-tricalcium phosphate) used in orthopedic applications were suspended in particulate form in physiologic saline, both as-received and supplemented with bovine serum albumin (BSA). Metal alloys were also treated with NaOH washing to study the effect of such a surface treatment on the zeta-potential. The NaOH wash was found to increase the zeta-potential for CoCrMo and Ti6Al4V, but there was a decrease in the magnitude of the zeta-potential for 316L stainless steel. When the metal alloy powders were suspended in BSA-supplemented physiologic saline, the zeta-potential as a function of pH increased, thereby increasing the electronegativity gap and increasing the propensity for bonding between each of the metal alloys and bone. This increase is likely due to matrix proteins in the BSA, which adsorb onto the metal alloy surfaces, promoting bone growth. With the addition of BSA to each bioceramic system, a uniform decrease in zeta-potential was observed. However, the electronegativity gap remained large in each case, maintaining the anticipation of bonding. zeta-Potential analysis is an effective predictor of biomaterial attraction to osteoblasts and bone, providing a useful in vitro method for predicting such interactions.

Elemental analysis of urinary calculi by laser induced plasma spectroscopy Fang, X., S. R. Ahmad, et al. (2005), Lasers Med Sci 20(3-4): 132-7.Abstract: Laser induced plasma spectroscopy (LIPS) has been applied to analyse and identify elemental constituents of urinary calculi. Measurements on seven different urinary stone samples were conducted and the concentrations of some key elemental species were estimated. The elements detected with the present system were: Calcium, Magnesium, Sodium, Samarium, Potassium and Lead. Absolute concentrations of the species were derived from pre-calibration of the system for each element. Their concentrations were found to be widely different in different samples. It was observed that the samples containing a significant amount of lead have large proportion of calcium. It has been established that LIPS would allow real time clinic measurements of elemental contents and the concentrations in the biomaterials without sample preparation. The technique has the potential for routine clinic applications in urological disorder diagnosis.

Elevation of the maxillary sinus floor with hydraulic pressure Sotirakis, E. G. and A. Gonshor (2005), J Oral Implantol 31(4): 197-204.Abstract: This study describes a new method using hydraulic pressure to elevate the antral floor for bone grafting between the sinus floor and the schneiderian membrane before placement of endosseous osseointegrated implants. The method was first modeled experimentally in hen eggs, acting as a surrogate sinus, and then in human cadaver preparations. Several clinical case reports are also presented. This technique successfully combines the advantages of the Caldwell-Luc window a pproach, which permits the placement of high bone graft volume, and the simplicity of the osteotome technique by way of the alveolar ridge crest.

Elimination of the friction effects in unconfined compression tests of biomaterials and soft tissues Wu, J. Z., R. G. Dong, et al. (2004), Proc Inst Mech Eng [H] 218(1): 35-40.Abstract: The mechanical properties of biomaterials and soft tissues are determined conventionally using unconfined compression tests. In such tests, frictionless specimen/platen contact in unconfined compression tests has to be assumed in determining the material properties of the materials. Previous theoretical analysis demonstrated, however, that the effects of the friction at the specimen/platen contact interface on the measured stress responses are non-negligible. In this study, a computational approach was proposed to eliminate the effects of friction. The friction coefficient between the specimen and the compression platens is measured first. Using a finite element model, the stress-strain relationship, without the influence of the friction effects, can be derived from the experimental data obtained in conventional unconfined compression tests. In order to validate the proposed approach, unconfined compressive tests of rubber have been performed.

Elution study of unreacted Bis-GMA, TEGDMA, UDMA, and Bis-EMA from light-cured dental resins and resin composites using HPLC Sideridou, I. D. and D. S. Achilias (2005), J Biomed Mater Res B Appl Biomater 74(1): 617-26.Abstract: In the present work the elution of residual monomers from light-cured dental resins and resin composites into a 75% ethanol:water solution was studied using High-Performance Liquid Chromatography (HPLC). The resins studied were made by light-curing of bisphenol A glycol dimethacrylate (Bis-GMA), triethylene glycol dimethacrylate (TEGDMA), urethane dimethacrylate (UDMA), ethoxylated bisphenol A glycol dimethacrylate [Bis-EMA(4)] and mixtures of these monomers. The resin composites were made from two commercial light-cured restorative materials (Z100 MP and Filtek Z250), the resin matrix of which is based on copolymers of these monomers. The effect of the curing time on the amount of monomers eluted was investigated. The concentration of the extractable monomers was determined at several immersion periods from 3 h to 30 days. For all the materials studied, it was observed that the chemical structure of the monomers used for the preparation of the resins, which defines the chemical and physical structure of the corresponding resin, directly affects the amount of eluted monomers, as well as the time needed for the elution of this amount. In the case of composites, it seems that the elution process it is not influenced by the presence of filler.